Multiple clocking modes for a CCD imager

ABSTRACT

A CCD image sensor includes vertical CCD shift registers and gate electrodes disposed over the vertical CCD shift registers. The gate electrodes are divided into distinct groups of gate electrodes. The CCD image sensor is adapted to operate in an accumulation mode and a charge transfer mode, an accumulation mode and a charge shifting mode, or an accumulation mode, a charge transfer mode, and a charge shifting mode. The charge transfer mode has an initial charge transfer phase and a final charge transfer phase. The charge shifting mode has an initial charge shifting phase and a final charge shifting phase.

CROSS REFERENCE TO RELATED APPLICATIONS

Reference is made to commonly-assigned, U.S. patent application Ser. No.13/241,500, entitled “MULTIPLE CLOCKING MODES FOR A CCD IMAGER”, Ser.No. 13/241,526, entitled “MULTIPLE CLOCKING MODES FOR A CCD IMAGER”,Ser. No. 13/241,547, entitled “MULTIPLE CLOCKING MODES FOR A CCDIMAGER”, all filed concurrently herewith.

TECHNICAL FIELD

The present invention relates to image sensors for use in digitalcameras and other types of image capture devices, and more particularlyto Charge-Coupled Device (CCD) image sensors. Still more particularly,the present invention relates to multiple clocking modes for a CCD imagesensor.

BACKGROUND

FIG. 1 is a simplified plan view of a prior art interline charge-coupleddevice (CCD) image sensor. Image sensor 100 includes photodetectors 102arranged in rows and columns to form an imaging area 104. A vertical CCD(VCCD) shift register 106 is disposed between the columns ofphotodetectors 102. Charge packets 108 accumulate in the photodetectors102 in response to incident light. The charge packets are transferred torespective shift register elements 110 in VCCD shift registers 106 andshifted one row at a time to horizontal CCD (HCCD) shift register 112.For simplicity, only one column of charge packets 108 is depicted inFIG. 1. Once in the HCCD shift register 112, the charge packets 108 areserially shifted through HCCD shift register 112 to output circuit 114.

FIG. 2 is a cross-sectional view of VCCD shift register 106 along lineA-A shown in FIG. 1. VCCD shift register 106 is depicted as a two-phaseCCD, where two distinct gate electrodes 200, 202 are associated witheach row of photodetectors. The first gate electrode 200 is clocked withsignal V1 and the second gate electrode 202 with signal V2.

VCCD shift register 106 is built on an n-type substrate 204 with ap-type layer 206 disposed between substrate 204 and n-type buriedchannel 208. The clock signals V1 and V2 alter the potential energywithin buried channel 208 to control the shifting of charge packetsthrough the VCCD shift register 106. With an n-type buried channel, themajority charge carriers are electrons that form the charge packets andflow in the n-type buried channel 208. Holes, the minority chargecarrier, will flow in the p-type layer 206.

As discussed earlier, the charge packets shifted through buried channel208 are generated by photons (i.e., light). In an interline CCD imagesensor, photons can also produce undesirable electrons known as darkcurrent in the VCCD shift registers. Accumulation mode clocking can beused to reduce the amount of dark current generated in the VCCDs.Accumulation mode clocking maintains all of the gate electrodes 200, 202at a negative voltage with respect to substrate 204 prior totransferring charge packets from the photodetectors to the VCCD shiftregisters. This causes holes to accumulate at the surface of the buriedchannel 208 under the gate electrodes 200, 202. The abundance of holesat the surface suppresses the generation of dark current. Charge packetsare then transferred to the VCCD shift registers and gate electrodes 200and 202 alternately clocked at higher voltage levels to shift the chargepackets through the VCCD shift registers 106. The alternating clockingpatterns repeat until all of the charge packets have been shiftedthrough the VCCD shift registers 106. A description of the benefits ofaccumulation mode clocking of CCD's may be found in U.S. Pat. No.4,963,952 and in the book entitled “Solid-State Imaging withCharge-Coupled Devices” by Albert J. P. Theuwissen.

Because p-type layer 206 is a thin layer confined between substrate 204and n-type buried channel 208, p-type layer 206 cannot easily act as asource or sink of holes. So when gate electrodes 200, 202 are clockedinto accumulation mode, holes flow from well contact 210 at theperimeter of the vertical CCD shift registers through p-type layer 202.The distances the holes must travel from well contact 210 can be long,and p-type layer 202 has a high resistance to the flow of holes.

FIG. 3 illustrates an equivalent circuit of VCCD shift registers acrossa row in an interline CCD image sensor. The nth gate electrode (gateelectrode n) has a capacitance to p-type layer 206 given by C. P-typelayer 206 has a resistance from well contact 210 to the nth gateelectrode given by (n×R). When the nth gate electrode is clocked intoaccumulation or depletion, the amount of time it takes for holes to flowfrom well contact 210 is related to the product of (n×R)×(n×C)=n²×RC.For large area CCD image sensors, this amount of time is too long andreduces the advantage of accumulation mode clocking.

Additionally, when only one clock signal, such as V1, has a rising edgefrom a low voltage (e.g., −9 V) to a higher voltage (e.g., 0 V), thevoltage on the resistors will not stay at ground (GND). Instead, thevoltage on the resistors will “bounce” positive with the V1 clock edgeand slowly return back to ground. This ground bounce produces poorcharge shifting through the VCCD shift registers.

U.S. Pat. Nos. 6,586,784 and 6,995,795 address the problem of groundbounce by implementing the timing pattern shown in FIG. 4 foraccumulation mode clocking. The clock signals V1 and V2 are clocked tothree different voltage levels, a negative −15 volts (V), a negative −9V, and zero V. During time T0, both the V1 and V2 clock signals are setat −9 V allowing holes to accumulate at the surface of the buriedchannel. At the transition from time T0 to time T1, the V2 clock signalhas a negative going voltage transition 400 to compensate the positivegoing transition 402 on the V1 clock signal. These compensated voltagetransitions can prevent ground bounce by causing no net flow of holesthrough the p-type layer (e.g. layer 206). This solution, however, canhave a serious problem. The −15 V on the clock signals is very negativeand can significantly reduce the lifetime of the gate oxides. The −15 Vcan also cause charge injection through the gate oxide directly into theCCD channel.

SUMMARY

In one aspect, a CCD image sensor includes vertical CCD shift registersand gate electrodes disposed over the vertical CCD shift registers. Thegate electrodes are divided into distinct groups of gate electrodes. TheCCD image sensor is adapted to operate in a charge shifting mode and inan accumulation mode. In the accumulation mode, an accumulation clocksignal is applied to all of the gate electrodes. In an initial chargeshifting phase of the charge shifting mode, a depletion clock signal isapplied to only one gate electrode in each distinct group of gateelectrodes while substantially simultaneously applying a compensationclock signal to all of the remaining gate electrodes in each distinctgroup of gate electrodes. A collective voltage transition of thecompensation clock signal on the remaining gate electrodes in eachdistinct group of gate electrodes substantially compensates for avoltage transition of the depletion clock signal on the one gateelectrode in each distinct group of gate electrodes.

In a final charge shifting phase of the charge shifting mode, thedepletion clock signal is applied successively or cyclically to adifferent one gate electrode in each distinct group of gate electrodesat each time step while substantially simultaneously applying thecompensation clock signal to the gate electrode clocked by the depletionclock signal at the previous time step and maintaining the compensationclock signal on the remaining gate electrodes in each distinct group ofgate electrodes. A voltage transition of the depletion clock signal oneach different one gate electrode in each distinct group of gateelectrodes is substantially compensated by a voltage transition of thecompensation clock signal on the gate electrode clocked by the depletionclock signal at the previous time step.

In another aspect, a CCD image sensor includes vertical CCD shiftregisters and gate electrodes disposed over the vertical CCD shiftregisters. The gate electrodes are divided into distinct groups of gateelectrodes. A method for operating the CCD image sensor includesapplying, at a first time period, an accumulation clock signal having afirst voltage level to all of the gate electrodes disposed over thevertical CCD shift registers for accumulating minority charge carriers.At a second time period, a depletion clock signal having a differentsecond voltage level is applied to a respective one of the gateelectrodes in each distinct group of gate electrodes while acompensation clock signal having a different third voltage level issubstantially simultaneously applied to all of the remaining gateelectrodes in each distinct group of gate electrodes. A differencebetween the first voltage level and the second voltage level produced atthe respective one of the gate electrodes is compensated by a differencebetween the first voltage level and the third voltage level produced atthe remaining gate electrodes in each distinct repeating group of gateelectrodes. At a third time period, the depletion clock signal havingthe second voltage level is applied to another respective one of thegate electrodes in each distinct repeating group of gate electrodeswhile the compensation clock signal having the third voltage level issubstantially simultaneously applied to the previous respective one ofthe gate electrodes clocked by the depletion clock signal in eachdistinct group of gate electrodes. A difference between the thirdvoltage level and the second voltage level produced at the anotherrespective one of the gate electrodes is compensated by a differencebetween the second voltage level and the third voltage level produced atthe previous respective one of the gate electrodes in each distinctgroup of gate electrodes.

In another aspect, a CCD image sensor includes vertical CCD shiftregisters and gate electrodes disposed over the vertical CCD shiftregisters. The gate electrodes are divided into distinct repeatinggroups of gate electrodes. A method for operating the CCD image sensorincludes applying, at a first time period, an accumulation clock signalhaving a first voltage level to all of the gate electrodes of thevertical shift registers. At a second time period, a depletion clocksignal having a different second voltage level is applied to arespective one of the gate electrodes in each distinct repeating groupof gate electrodes while a compensation clock signal having a differentthird voltage level is substantially simultaneously applied to theremaining gate electrodes in each distinct repeating group of gateelectrodes. A difference between the second voltage level and the thirdvoltage level is greater than a difference between the second voltagelevel and the first voltage level and a difference between the secondvoltage level and the first voltage level is greater than a differencebetween the third voltage level and the first voltage level.

In another aspect, each gate electrode (n) has a capacitance C_(n). Avoltage change on gate electrode n is given by ΔV_(n). At each timestep, the clock signals applied to the gate electrodes in each distinctgroup of gate electrodes are patterned or determined so that the sum ofproducts of the capacitances and voltage changes is substantially zero.The sum of products can be represented by the equation ΣC_(n)ΔV_(n)≈0.

In another aspect, a CCD image sensor is adapted to operate in a chargetransfer mode and in an accumulation mode. The CCD image sensor includesvertical CCD shift registers and gate electrodes disposed over thevertical CCD shift registers. The gate electrodes are divided intodistinct groups of gate electrodes. A method for operating the CCD imagesensor includes in an initial charge transfer phase of the chargetransfer mode, applying at a first time step an intermediate clocksignal to a fraction of the gate electrodes in each distinct group ofgate electrodes while substantially simultaneously applying anaccumulation clock signal to the remaining gate electrodes in eachdistinct group of gate electrodes. At a second time step, a transferclock signal is applied to at least one of the gate electrodes in eachdistinct group of gate electrodes previously clocked by the intermediateclock signal while the accumulation clock signal is substantiallysimultaneously applied to the remaining gate electrodes in each distinctgroup of gate electrodes previously clocked by the intermediate clocksignal. In a final charge transfer phase of the charge transfer mode,the transfer clock signal is applied successively to a differentfraction of the gate electrodes in each distinct group of gateelectrodes at each time step while the accumulation clock signal issubstantially simultaneously applied to each gate electrode previouslyclocked by the transfer clock signal and the accumulation clock signalis maintained on the remaining gate electrodes in each distinct group ofgate electrodes.

In another aspect, a CCD image sensor includes photodetectors andvertical CCD shift registers disposed between columns of photodetectors.Gate electrodes are disposed over the vertical CCD shift registers andthe gate electrodes are divided into distinct groups of gate electrodes.A method for transferring charge packets from the photodetectors to thevertical CCD shift registers in the CCD image sensor includes applyingat a first time period an intermediate clock signal having a firstvoltage level to a portion of the gate electrodes in each distinctrepeating group of gate electrodes. At a second time period,transferring charge packets from a portion of the photodetectors torespective vertical CCD shift registers by applying a transfer clocksignal having a different second voltage level to a portion of the gateelectrodes previously clocked by the intermediate clock signal andapplying an accumulation clock signal having a different third voltagelevel to the remaining portion of the gate electrodes previously clockedby the intermediate clock signal such that a voltage transition on thegate electrodes clocked by the transfer clock signal is compensated by avoltage transition on the gate electrodes clocked by the accumulationclock signal.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention are better understood with reference to thefollowing drawings. The elements of the drawings are not necessarily toscale relative to each other.

FIG. 1 is a simplified plan view of a prior art interline charge-coupleddevice (CCD) image sensor;

FIG. 2 is a cross-sectional view of VCCD shift register 106 along lineA-A shown in FIG. 1;

FIG. 3 illustrates an equivalent circuit of VCCD shift registers acrossa row in an interline CCD image sensor;

FIG. 4 is a prior art timing pattern used to reduce well bounce;

FIG. 5 is a simplified block diagram of an image capture device in anembodiment in accordance with the invention;

FIGS. 6A-6B are simplified plan views of an imaging area for aninterline CCD image sensor in an embodiment in accordance with theinvention;

FIG. 7 illustrates a group of twelve gate electrodes and associatedclocking diagrams in an embodiment in accordance with the invention;

FIG. 8 is an exemplary clocking diagram for the twelve gate electrodesillustrated in FIG. 7;

FIG. 9 depicts one example of a clocking diagram for four-phase verticalCCD shift registers in an embodiment in accordance with the invention;

FIG. 10 illustrates a first example of a clocking diagram fortransferring charge from the photodetectors to respective shift registerelements in the VCCD shift registers in an interline CCD image sensor inan embodiment in accordance with the invention; and

FIG. 11 depicts a second example of a clocking diagram for transferringcharge from the photodetectors to respective shift register elements inthe VCCD shift registers in an interline CCD image sensor in anembodiment in accordance with the invention.

DETAILED DESCRIPTION

Throughout the specification and claims the following terms take themeanings explicitly associated herein, unless the context clearlydictates otherwise. The meaning of “a,” “an,” and “the” includes pluralreference, the meaning of “in” includes “in” and “on.” The term“connected” means either a direct electrical connection between theitems connected or an indirect connection through one or more passive oractive intermediary devices. The term “circuit” means either a singlecomponent or a multiplicity of components, either active or passive,that are connected together to provide a desired function. The term“signal” means at least one current, voltage, or data signal.

Additionally, directional terms such as “on”, “over”, “top”, “bottom”,“left”, “right”, are used with reference to the orientation of theFigure(s) being described. Because components of embodiments of thepresent invention can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration only and is in no way limiting. When used in conjunctionwith layers of an image sensor wafer or corresponding image sensor, thedirectional terminology is intended to be construed broadly, andtherefore should not be interpreted to preclude the presence of one ormore intervening layers or other intervening image sensor features orelements. Thus, a given layer that is described herein as being disposedor formed on or over another layer may be separated from the latterlayer by one or more additional layers. When used in conjunction withthe construction or operation of an image sensor, the directionalterminology is intended to be construed broadly, and therefore shouldnot be interpreted to preclude alternate constructions or operations.

Referring to the drawings, like numbers indicate like parts throughoutthe views.

FIG. 5 is a simplified block diagram of an image capture device in anembodiment in accordance with the invention. Image capture device 500 isimplemented as a digital camera in FIG. 5. Those skilled in the art willrecognize that a digital camera is only one example of an image capturedevice that can utilize an image sensor incorporating the presentinvention. Other types of image capture devices, such as, for example,cell phone cameras and digital video camcorders, can be used with thepresent invention.

In digital camera 500, light 502 from a subject scene is input to animaging stage 504. Imaging stage 504 can include conventional elementssuch as a lens, a neutral density filter, an iris and a shutter. Light502 is focused by imaging stage 504 to form an image on image sensor506. Image sensor 506 captures one or more images by converting theincident light into electrical signals. Image sensor 506 is implementedas a CCD image sensor. Clock driver 508 produces clock signals that areused by image sensor 506. With respect to the present invention, clockdriver 508 produces clock signals that are used by image sensor 506 foran accumulation mode, a charge transfer mode, or a charge shifting mode.

Digital camera 500 further includes processor 510, memory 512, display514, and one or more additional input/output (I/O) elements 516.Although shown as separate elements in the embodiment of FIG. 5, imagingstage 504 may be integrated with image sensor 506, and possibly one ormore additional elements of digital camera 500, to form a compact cameramodule.

Processor 510 may be implemented, for example, as a microprocessor, acentral processing unit (CPU), an application-specific integratedcircuit (ASIC), a digital signal processor (DSP), or other processingdevice, or combinations of multiple such devices. Various elements ofimaging stage 504 and image sensor 506 can be controlled by timingsignals or other signals supplied from processor 510. The function ofclock driver 508 can be performed by processor 510 in some embodimentsin accordance with the invention. In other embodiments in accordancewith the invention, clock driver 508 or a processor performing thefunction of clock driver 508 can be integrated with image sensor 506.

Memory 512 can be configured as any type of memory, such as, forexample, random access memory (RAM), read-only memory (ROM), Flashmemory, disk-based memory, removable memory, or other types of storageelements, in any combination. A given image captured by image sensor 506may be stored by processor 510 in memory 512 and presented on display514. Additionally, the function of clock driver 508 can be performed bymemory 512 and processor 510 in another embodiment in accordance withthe invention. The clock signals for the accumulation mode, the chargetransfer mode, or the charge shifting mode can be stored in memory 512and read out by processor 510. Memory 512, processor 510, or both memory512 and processor 510 can be integrated with image sensor 506 inembodiments in accordance with the invention.

Display 514 is typically an active matrix color liquid crystal display(LCD), although other types of displays may be used. The additional I/Oelements 516 may include, for example, various on-screen controls,buttons or other user interfaces, network interfaces, or memory cardinterfaces.

It is to be appreciated that the digital camera shown in FIG. 5 maycomprise additional or alternative elements of a type known to thoseskilled in the art. Elements not specifically shown or described hereinmay be selected from those known in the art. As noted previously, thepresent invention may be implemented in a wide variety of image capturedevices. Also, certain aspects of the embodiments described herein maybe implemented at least in part in the form of software executed by oneor more processing elements of an image capture device. Such softwarecan be implemented in a straightforward manner given the teachingsprovided herein, as will be appreciated by those skilled in the art.

Referring now to FIGS. 6A-6B, there are shown simplified plan views ofan imaging area for an interline CCD image sensor in an embodiment inaccordance with the invention. Imaging area 600 includes vertical CCD(VCCD) shift registers 602. A column of photodetectors 604 is adjacentto each VCCD shift register 602. In the illustrated embodiment, twodistinct gate electrodes 606, 608 are associated with each row. The twogate electrodes 606, 608 are disposed over VCCD shift registers 602 andare used to shift charge packets through the VCCD shift registers. Forsimplicity and clarity, gate electrodes 606, 608 are shown disposed overonly a portion of imaging area 600. Signal lines V1 through V12(collectively 610) are used to apply independent clock signals to gateelectrodes 606, 608.

FIG. 6B depicts a more detailed view of the arrangement of the gateelectrodes 606, 608 disposed over imaging area 600. The gate electrodes606, 608 do not cover photodetectors 604. Instead, the gate electrodes606, 608 are disposed around and extend between photodetectors 604 suchthat gate electrodes 606, 608 are disposed over VCCD shift registers602. In practice, in a multi-phase CCD, such as with a two phase CCD,one set of gate electrodes overlaps another set of gate electrodes. Thisis not shown in FIGS. 6A-6B for simplicity. Other embodiments inaccordance with the invention can dispose the gate electrodes over boththe photodetectors and the VCCD shift registers. In full frame CCD imagesensors, the gate electrodes are disposed over the VCCD shift registerssince the shift register elements in the VCCD shift registers arephotosensitive and collect charge packets.

Although FIG. 6A depicts a repeating pattern of twelve signal lines thatare applied to twelve gate electrodes with two gate electrodes per rowof photodetectors, in practice there is a repeating pattern of N numberof gate electrodes with M gate electrodes per row in embodiments inaccordance with the invention. Each set of N gate electrodes form adistinct group of gate electrodes, and each group has M number of gateelectrodes per row of photodetectors, where M is greater than one andless than N in an embodiment in accordance with the invention. In theembodiment shown in FIG. 6A, each distinct group of gate electrodes hastwelve gate electrodes (N=12) with two gate electrodes (M=2) associatedwith each row of photodetectors. Other embodiments in accordance withthe invention can group the gate electrodes differently, such as, forexample, into groups of eight gate electrodes (N=8) with four gateelectrodes per row (M=4).

The number of independent clock signals equals N, the number of gateelectrodes in each distinct group of gate electrodes.

FIG. 7 depicts a group of twelve gate electrodes (N=12) and associatedpotential energy clocking diagrams in an embodiment in accordance withthe invention. In the illustrated embodiment, the group of twelve gateelectrodes 700 (N=12) is associated with six rows in an imaging areabecause the VCCD shift registers are implemented as two-phase (M=2) VCCDshift registers. Other embodiments in accordance with the invention canimplement the VCCD shift registers with any number of phases.

The group of twelve gate electrodes 700 is included in a larger imagingarea (not shown). The charge shifting process shifts only one chargepacket forward (i.e., toward the horizontal CCD shift register) at eachtime step. Each gate electrode only spends a short amount of time indepletion mode. By way of example only, each gate electrode can spendonly two microseconds in depletion mode. The gate electrode placed indepletion mode ripples through all twelve gate electrodes to shift acharge packet by only one gate electrode. For example, in a two-phaseCCD image sensor where each row has two gate electrodes, the clock pulseripples through the gate electrodes twice to advance a charge packet byone full row.

FIG. 8 is an exemplary clocking diagram for the twelve gate electrodesillustrated in FIG. 7. FIG. 8 is described in conjunction with thecharge shifting diagrams in FIG. 7. The gate electrodes are clockedindependently in an embodiment in accordance with the invention. Priorto time T1, all of the gate electrodes are placed in accumulation modeby applying an accumulation clock signal (V_(ACC)) to the gateelectrodes. Minority carriers (e.g., holes) accumulate at the surface ofthe buried channel in the VCCD shift registers during the accumulationmode. Charge packets 702, 704, 706, 708, 710, 712 are stored in theburied channel under gate electrodes V3, V5, V7, V9, V11, V1respectively.

At time T1, only one gate electrode is placed in depletion mode byapplying a depletion clock signal (V_(DEP)) to that gate electrode. Inthe illustrated embodiment of FIG. 8, gate electrode V2 is placed indepletion mode. At substantially the same time as the rising edge of theV_(DEP) clock signal, a compensation clock signal (V_(COMP)) having afalling edge at time T1 is applied to the remaining gate electrodes inthe group 700. As shown in FIG. 7, charge packet 702 shifts forward onegate electrode in response to the application of the V_(DEP) clocksignal to gate electrode V2. Charge packet 702 shifts from under gateelectrode V3 to under gate electrode V2.

In the FIG. 8 embodiment, V_(ACC) is −9 volts, V_(DEP) is 0 volts, andV_(COMP) is −9.8 volts so that V_(COMP)<V_(ACC)<V_(DEP). The voltagelevel of V_(ACC) is between the voltage levels of V_(COMP) and V_(DEP).Application of the V_(DEP) clock signal clocks only one gate electrodein each distinct group of gate electrodes from −9 volts to 0 volts, adifference of 9 volts. To compensate for the 9 volt rising edge of theV_(DEP) clock signal, the remaining eleven gate electrodes in eachdistinct group of gate electrodes are substantially simultaneouslyclocked with clock signal V_(COMP). The voltage on each of the remainingeleven gate electrodes transitions from −9 volts to −9.8 volts at timeT1, a difference of −0.8 volts. Thus, the 9 V voltage transition of theV_(DEP) clock signal is compensated by the eleven −0.8 V voltagetransitions of the V_(COMP) clock signal on gate electrodes V1 andV3-V12. The magnitude of the voltage transition in one direction orpolarity (e.g., positive) on one gate electrode in group 700 iscompensated by a collective magnitude voltage transition in an oppositedirection or polarity (e.g., negative) on the remaining gate electrodesin group 700.

Referring to time T2 in FIG. 8, only gate electrode V4 in each group ofgate electrodes is placed in depletion mode by applying the depletionclock signal (V_(DEP)) to the gate electrode. At substantially the sametime as the rising edge of the V_(DEP) clock signal, the compensationclock signal (V_(COMP)) is applied to gate electrode V2, the gateelectrode clocked by the V_(DEP) clock signal at the previous time step(time T1). The V_(COMP) clock signal is maintained on gate electrodesV1, V3, and V5-V12 in group 700. The +9.8 V voltage transition (therising edge) of the V_(DEP) clock signal on gate electrode V4 iscompensated by the −9.8 V voltage transition (the falling edge) of theV_(COMP) clock signal on gate electrode V2.

As shown in FIG. 7, charge packet 704 shifts forward one gate electrodein response to the application of the depletion clock signal (V_(DEP))to gate electrode V4. Charge packet 704 shifts from under gate electrodeV5 to under gate electrode V4.

At time T3, only gate electrode V6 in group 700 is placed in depletionmode by applying V_(DEP) clock signal to the gate electrode. Atsubstantially the same time as the rising edge of the V_(DEP) clocksignal, V_(COMP) is applied to gate electrode V4, the gate electrodeclocked by the V_(DEP) clock signal at the previous time step (time T2).The V_(COMP) clock signal is maintained on gate electrodes V1-V3, V5,and V7-V12 in group 700. The +9.8 V voltage transition (the rising edge)of the V_(DEP) clock signal on gate electrode V6 is compensated by the−9.8 V voltage transition (the falling edge) of the V_(COMP) clocksignal on gate electrode V4.

As shown in FIG. 7, charge packet 706 shifts forward one gate electrodein response to the application of the depletion clock signal (V_(DEP))to gate electrode V6. Charge packet 706 shifts from under gate electrodeV7 to under gate electrode V6.

At time T4, only gate electrode V8 is placed in depletion mode byapplying V_(DEP) to the gate electrode. At substantially the same timeas the rising edge of the V_(DEP) clock signal on gate electrode V8,V_(COMP) is applied to gate electrode V6, the gate electrode clocked bythe V_(DEP) clock signal at the previous time step (time T3). TheV_(COMP) clock signal is maintained on gate electrodes V1-V5, V7, andV9-V12 in group 700. The +9.8 V voltage transition (the rising edge) ofthe V_(DEP) clock signal on gate electrode V8 is compensated by the −9.8V voltage transition (the falling edge) of the V_(COMP) clock signal ongate electrode V6.

As shown in FIG. 7, charge packet 708 shifts forward one gate electrodein response to the application of the depletion clock signal (V_(DEP))to gate electrode V8. Charge packet 708 shifts from under gate electrodeV9 to under gate electrode V8.

At time T5, only gate electrode V10 is placed in depletion mode byapplying V_(DEP) to the gate electrode. At substantially the same timeas the rising edge of the V_(DEP) clock signal, the clock signalV_(COMP) is applied to gate electrode V8, the gate electrode clocked bythe V_(DEP) clock signal at the previous time step (time T4). TheV_(COMP) clock signal is maintained on gate electrodes V1-V7, V9, V11,and V12 in group 700. The +9.8 V voltage transition (the rising edge) ofthe V_(DEP) clock signal on gate electrode V10 is compensated by the−9.8 V voltage transition (the falling edge) of the V_(COMP) clocksignal on gate electrode V8.

As shown in FIG. 7, charge packet 710 shifts forward one gate electrodein response to the application of the depletion clock signal (V_(DEP))to gate electrode V10. Charge packet 710 shifts from under gateelectrode V11 to under gate electrode V10.

At time. T6, only gate electrode V12 is placed in depletion mode byapplying V_(DEP) to the gate electrode. At substantially the same timeas the rising edge of the V_(DEP) clock signal, V_(COMP) is applied togate electrode V10, the gate electrode clocked by the V_(DEP) clocksignal at the previous time step (time T5). The V_(COMP) clock signal ismaintained on gate electrodes V1-V9 and V11 in group 700. The +9.8 Vvoltage transition (the rising edge) of the V_(DEP) clock signal on gateelectrode V12 is compensated by the −9.8 V voltage transition (thefalling edge) of the V_(COMP) clock signal on gate electrode V10.

As shown in FIG. 7, charge packet 712 shifts forward one gate electrodein response to the application of the depletion clock signal (V_(DEP))to gate electrode V12. Charge packet 712 shifts from under gateelectrode V1 to under gate electrode V12. Gate electrode V1 (see 714) isin the adjacent group of twelve gate electrodes.

At the end of time T6, all of the charge packets have shifted forwardone gate electrode. In a two-phase CCD shift register, the chargepackets must move forward two gate electrodes to shift to the next row.So the clock signals depicted in FIG. 8 continue through six additionaltime steps. At time T7, only gate electrode V1 is placed in depletionmode by applying V_(DEP) to the gate electrode. At substantially thesame time as the rising edge of the V_(DEP) clock signal, V_(COMP) isapplied to gate electrode V12, the gate electrode clocked by the V_(DEP)clock signal at the previous time step (time T6). The V_(COMP) clocksignal is maintained on gate electrodes V2-V11 in group 700.

Charge packet 702 shifts forward one gate electrode in response to theapplication of the depletion clock signal (V_(DEP)) to gate electrode V1(not shown). Charge packet 702 shifts from under gate electrode V2 tounder gate electrode V1. The +9.8 V voltage transition (the rising edge)of the V_(DEP) clock signal on gate electrode V1 is compensated by the−9.8 V voltage transition (the falling edge) of the V_(COMP) clocksignal on gate electrode V12.

At time T8, only gate electrode V3 is placed in depletion mode byapplying V_(DEP) to the gate electrode. At substantially the same timeas the rising edge of the V_(DEP) clock signal, V_(COMP) is applied togate electrode V1, the gate electrode clocked by the V_(DEP) clocksignal at the previous time step (time T7). The V_(COMP) clock signal ismaintained on gate electrodes V2 and V4-V12 in group 700.

Charge packet 704 shifts forward one gate electrode in response to theapplication of the V_(DEP) clock signal to gate electrode V3 (notshown). Charge packet 704 shifts from under gate electrode V4 to undergate electrode V3. The +9.8 V voltage transition (the rising edge) ofthe depletion clock signal (V_(DEP)) on gate electrode V3 is compensatedby the −9.8 V voltage transition (the falling edge) of the V_(COMP)clock signal on gate electrode V1.

At time T9, only gate electrode V5 is placed in depletion mode byapplying V_(DEP) to the gate electrode. At substantially the same timeas the rising edge of the V_(DEP) clock signal, V_(COMP) is applied togate electrode V3, the gate electrode clocked by the V_(DEP) clocksignal at the previous time step (time T8). The V_(COMP) clock signal ismaintained on gate electrodes V1, V2, V4 and V6-V12 in group 700.

Charge packet 706 shifts forward one gate electrode in response to theapplication of the V_(DEP) clock signal to gate electrode V5 (notshown). Charge packet 706 shifts from under gate electrode V6 to undergate electrode V5. The +9.8 V voltage transition (the rising edge) ofthe depletion clock signal (V_(DEP)) is compensated by the −9.8 Vvoltage transition (the falling edge) of the V_(COMP) clock signal ongate electrode V3.

At time T10, only gate electrode V7 is placed in depletion mode byapplying V_(DEP) to the gate electrode. At substantially the same timeas the rising edge of the V_(DEP) clock signal, V_(COMP) is applied togate electrode V5, the gate electrode clocked by the V_(DEP) clocksignal at the previous time step (time T9). The V_(COMP) clock signal ismaintained on gate electrodes V1-V4, V6 and V8-V12 in group 700.

Charge packet 708 shifts forward one gate electrode in response to theapplication of the depletion clock signal (V_(DEP)) to gate electrode V7(not shown). Charge packet 708 shifts from under gate electrode V8 tounder gate electrode V7. The +9.8 V voltage transition (the rising edge)of the V_(DEP) clock signal on gate V7 is compensated by the −9.8 Vvoltage transition (the falling edge) of the V_(COMP) clock signal ongate electrode V5.

At time T11, only gate electrode V9 is placed in depletion mode byapplying V_(DEP) to the gate electrode. At substantially the same timeas the rising edge of the V_(DEP) clock signal, V_(COMP) is applied togate electrode V7, the gate electrode clocked by the V_(DEP) clocksignal at the previous time step. The V_(COMP) clock signal ismaintained on gate electrodes V1-V6, V8, and V10-V12 in group 700.

Charge packet 710 shifts forward one gate electrode in response to theapplication of the depletion clock signal (V_(DEP)) to gate electrode V9(not shown). Charge packet 710 shifts from under gate electrode V10 tounder gate electrode V9. The +9.8 V voltage transition (the rising edge)of the V_(DEP) clock signal on gate electrode V9 is compensated by the−9.8 V voltage transition (the falling edge) of the V_(COMP) clocksignal on gate electrode V7.

At time T12, only gate electrode V11 is placed in depletion mode byapplying V_(DEP) to the gate electrode. At substantially the same timeas the rising edge of the V_(DEP) clock signal, the clock signalV_(COMP) is applied to gate electrode V9, the gate electrode clocked bythe V_(DEP) clock signal at the previous time step (time T11). TheV_(COMP) clock signal is maintained on gate electrodes V1-V8, V10 andV12 in group 700.

Charge packet 712 shifts forward one gate electrode in response to theapplication of the depletion clock signal (V_(DEP)) to gate electrodeV11 (not shown). Charge packet 712 shifts from under gate electrode V12to under gate electrode V11. The +9.8 V voltage transition (the risingedge) of the V_(DEP) clock signal on gate electrode V11 is compensatedby the −9.8 V voltage transition (the falling edge) of the V_(COMP)clock signal on gate electrode V9.

At the end of time T12, all of the charge packets have shifted forwardtwo gate electrodes in the VCCD shift registers and the accumulationclock signal V_(ACC) is applied to all of the gate electrodes. Thepattern of clock signals depicted in FIG. 8 repeat until all of thecharge packets have been shifted out of the VCCD shift registers.

As described earlier, each gate electrode n has a capacitance C_(n). Avoltage transition on gate electrode n is given by ΔV_(n). In theembodiment of FIG. 8, the clock signals applied to the gate electrodesin each distinct group of gate electrodes are patterned or determined sothat the sum of products of the capacitances and voltage changes issubstantially zero. The sum of products can be represented by theequation ΣC_(n)ΔV_(n)≈0.

Referring now to FIG. 9, there is shown one example of a clockingdiagram for four-phase vertical CCD shift registers in an embodiment inaccordance with the invention. The timing diagram can be used, forexample, with a two-field interlaced CCD image sensor, where the gateelectrodes of the four phase vertical CCD shift register are spread outacross two rows resulting in two gate electrodes per row. In theillustrated clocking diagram, each distinct group of gate electrodesincludes four gate electrodes (N=4) with two gate electrodes per row(M=2) and the four gate electrodes are clocked independently. Theaccumulation clock signal V_(ACC) is −9 volts, the depletion clocksignal V_(DEP) is 0 volts, and the compensation clock signal V_(COMP) is−10 volts in the FIG. 9 embodiment (V_(COMP)<V_(ACC)<V_(DEP)). Thedifferent clock signals are determined so that the sum of products ofthe capacitances and voltage changes for at least a portion of aclocking cycle is substantially zero (ΣC_(n)ΔV_(n)≈0). As is describedin more detail later, in the illustrated embodiment the different clocksignals are determined so that the sum of products of the capacitancesand voltage changes during the final charge shifting phase issubstantially zero (ΣC_(n)ΔV_(n)≈0).

At time T1, only gate electrode V2 is placed in depletion mode byapplying the depletion clock signal V_(DEP) to the gate electrode. Atsubstantially the same time as the rising edge of the V_(DEP) clocksignal, the clock signal V_(COMP) is applied to the remaining gateelectrodes in the group. The voltage transition on gate electrode V2equals +9 volts while the voltage transition on gate electrodes V1, V3,and V4 combined equals −3 volts. Thus, the voltage transition on gateelectrode V2 is only partially compensated at time T1 in the illustratedembodiment.

Only one charge packet shifts forward one gate electrode in response tothe application of the depletion clock signal (V_(DEP)) to gateelectrode V2 (not shown). The charge packet shifts from under gateelectrode V3 to under gate electrode V2.

At time T2, only gate electrode V4 is placed in depletion mode byapplying the depletion clock signal V_(DEP) to the gate electrode. Atsubstantially the same time as the rising edge of the V_(DEP) clocksignal, the compensation clock signal V_(COMP) is applied to gateelectrode V2. Gate electrode V2 is the gate clocked by the clock signalV_(DEP) at the previous time step (time T1). V_(COMP) continues to beapplied to gate electrodes V1 and V3. The voltage transition (the risingedge) of V_(DEP) on gate electrode V4 equals +10 volts while the voltagetransition (the falling edge) of V_(COMP) on gate electrode V2 equals−10 volts. Thus, the voltage transition of V_(DEP) on gate electrode V4is fully compensated by the voltage transition of V_(COMP) on gateelectrode V2.

Only one charge packet shifts forward one gate electrode in response tothe application of the depletion clock signal (V_(DEP)) to gateelectrode V4 (not shown). The charge packet shifts from under gateelectrode V1 in the adjacent group to under gate electrode V4.

At time T3, only gate electrode V1 is placed in depletion mode byapplying the depletion clock signal V_(DEP) to the gate electrode. Atsubstantially the same time as the rising edge of the depletion clocksignal V_(DEP), the compensation clock signal V_(COMP) is applied togate electrode V4. Gate electrode V4 is the gate clocked by V_(DEP) atthe previous time step (time T2). The compensation clock signal V_(COMP)continues to be applied to gate electrodes V2 and V3. The voltagetransition (the rising edge) of V_(DEP) on gate electrode V1 is +10volts while the voltage transition (the falling edge) of V_(COMP) ongate electrode V4 is −10 volts. Thus, the voltage transition of V_(DEP)on gate electrode V1 is fully compensated by the voltage transition ofV_(COMP) on gate electrode V4 in the illustrated embodiment.

Only one charge packet shifts forward one gate electrode in response tothe application of the depletion clock signal V_(DEP) to gate electrodeV1 (not shown). The charge packet shifts from under gate electrode V2 tounder gate electrode V1.

At time T4, only gate electrode V3 is placed in depletion mode byapplying the depletion clock signal V_(DEP) to the gate electrode. Atsubstantially the same time as the rising edge of the depletion clocksignal V_(DEP), the compensation clock signal V_(COMP) is applied togate electrode V1. Gate electrode V1 is the gate electrode clocked byV_(DEP) at the previous time step (time T3). V_(COMP) continues to beapplied to gate electrodes V2 and V4. The voltage transition (the risingedge) of the depletion clock signal V_(DEP) on gate electrode V3 is +10volts while the voltage transition (the falling edge) of V_(COMP) ongate electrode V1 is −10 volts. Thus, the voltage transition of V_(DEP)on gate electrode V3 is compensated fully by the voltage transition ofV_(COMP) on gate electrode V1 in the illustrated embodiment.

At the end of time T4, all of the charge packets have shifted forwardtwo gate electrodes and the accumulation clock signal V_(ACC) is appliedto all of the gate electrodes. The voltage transition on gate electrodeV3 is −9 volts while the voltage transition on gate electrodes V1, V2,and V4 combined equals +3 volts. Thus, the voltage transition of V_(DEP)on gate electrode V3 is only partially compensated at time T5 in theillustrated embodiment.

There are two operating modes for a CCD image sensor in an embodiment inaccordance with the invention. One mode is an accumulation mode where anaccumulation clock signal is applied to all of the gate electrodes. Thismode is illustrated prior to time T1 and at time T13 in FIG. 8 and priorto time T1 and at time T5 in FIG. 9. Minority carriers (e.g., holes)accumulate at the surface of the buried channel in the VCCD shiftregisters during the accumulation mode.

The other mode is a charge shifting mode. The charge shifting modeincludes two phases, an initial charge shifting phase followed by afinal charge shifting phase. The initial charge shifting phase isdepicted at time T1 in FIGS. 8 and 9. During the initial charge shiftingphase, a depletion clock signal V_(DEP) is applied to only one gateelectrode in each distinct group of gate electrodes while substantiallysimultaneously applying a compensation clock signal V_(COMP) to all ofthe remaining gate electrodes in each distinct group of gate electrodes.The compensation by the collective voltage transitions of V_(COMP) cancompensate fully or partially for the voltage transition of V_(DEP) inembodiments in accordance with the invention.

The final charge shifting phase is depicted at times T2-T12 in FIG. 8and at times T2-T4 in FIG. 9. During the final charge shifting phase,the depletion clock signal V_(DEP) is applied successively or cyclicallyto a different one gate electrode in each distinct group of gateelectrodes at each time step while substantially simultaneously applyingthe compensation clock signal V_(COMP) to the gate electrode clocked bythe depletion clock signal V_(DEP) at the previous time step and whilemaintaining the accumulation clock signal V_(COMP) on the remaining gateelectrodes in each distinct group of gate electrodes. The voltagetransition of V_(DEP) is compensated fully by the voltage transition ofV_(COMP). The magnitude of the voltage transition in one direction orpolarity (e.g., positive) on the one gate electrode in each distinctgroup of gate electrodes is compensated by an equal magnitude voltagetransition in an opposite direction or polarity (e.g., negative) onanother gate electrode in each distinct group of gate electrodes.

In one embodiment in accordance with the invention, application of thedepletion clock signal V_(DEP) and application of the compensation clocksignal V_(COMP) cycle through the even numbered gate electrodes and thenthrough the odd numbered gate electrodes. For example, in the embodimentshown in FIG. 8, V_(DEP) is applied, in order, to gate electrode V2,gate electrode V4, gate electrode V6, gate electrode V8, gate electrodeV10, and gate electrode V12 before cycling through the odd numbered gateelectrodes V1, V3, V5, V7, V9, and V11. V_(COMP) is applied, in order,to gate electrode V2, gate electrode V4, gate electrode V6, gateelectrode V8, gate electrode V10, and gate electrode V12 before cyclingthrough the odd numbered gate electrodes V1, V3, V5, V7, V9, and V11.The V_(DEP) clock signal and the V_(COMP) clock signal can be applied toadjacent even numbered gate electrodes (e.g., gate electrode V4 and V2,respectively) and adjacent odd numbered gate electrodes (e.g., gateelectrode V7 and gate electrode V5, respectively). Other embodiments inaccordance with the invention can cycle through the gate electrodes ineach distinct group of gate electrodes differently. For example, theembodiment of FIG. 12 illustrates the gate electrodes being cycledthrough in a different order by the clocking diagram in FIG. 13, butstill accomplishing the same final charge shifting results as theembodiment of FIG. 8.

One advantage to the embodiments shown in FIGS. 8 and 9 is thecompensation clock signal V_(COMP) voltage is only −9.8 V and −10 V,respectively, compared to the −15 V of the prior art. The reliability ofthe gate oxides is improved by changing the most negative voltage of aclock signal to a smaller negative value.

Well bounce can be reduced or eliminated through the compensating timingpatterns shown and described in conjunction with FIGS. 8 and 9. Thecompensating clock signals in these timing patterns are applied to thegate electrodes used to shift charge packets through the VCCD shiftregisters. As described in more detail below, well bounce can also bereduced or eliminated through compensating clock signals applied to thegate electrodes used to transfer charge packets from the photodetectorsto the VCCD shift registers. The compensating clock signals used totransfer charge packets from the photodetectors to the VCCD shiftregisters can be used independent of, or in combination with, thecompensating clock signals applied to the gate electrodes to shiftcharge packets through the VCCD shift registers.

FIG. 10 illustrates a first example of a clocking diagram fortransferring charge from the photodetectors to respective shift registerelements in the VCCD shift registers in an interline CCD image sensor inan embodiment in accordance with the invention. The clocking diagram issuitable for use in a CCD image sensor having twelve gate electrodes(N=12) in each group of gate electrodes. The clocking diagram of FIG. 10will be described in conjunction with the vertical CCD shift registergate electrode arrangement shown in FIG. 7. Thus, the VCCD shiftregisters are implemented as two-phase VCCD shift registers where twogate electrodes are associated with each row of photodetectors.

Prior to time T1, the accumulation clock signal V_(ACC) is applied toall of the gate electrodes to place the gate electrodes in accumulationmode. To transfer charge from the photodetectors to the VCCD shiftregisters, a large voltage change is applied to half of the gateelectrodes because all gate electrodes are in accumulation mode. By wayof example only, when V_(ACC) is −9 volts and a transfer clock signalV_(TR) of +9 volts is needed to transfer charge from the photodetectors,a voltage transition of +18 volts must be applied to half of the gateelectrodes to transfer the charge from the photodetectors to the VCCDshift registers. The +18 V voltage transition can produce a large amountof undesirable well bounce. The clocking diagram shown in FIG. 10reduces the amount of well bounce when transferring charge from thephotodetectors to the VCCD shift registers.

At time T1, an intermediate clock signal V_(INT) is applied to afraction of the gate electrodes. In the illustrated embodiment, V_(INT)is applied to gate electrodes V1, V4, V7, and V10. These four gateelectrodes, V1, V7, V4, V10, have uncompensated voltage transitions(e.g., rising edges) at time T1 because there is no voltage transitionon the remaining gate electrodes V2, V3, V5, V6, V8, V9, V11, and V12.The voltage transitions on gate electrodes V1, V7, V4, and V10 is +9volts (from −9 volts to 0 volts). In the illustrated embodiment, a timedelay between time T1 and time T2 allows the well to settle before thenext voltage change occurs at time T2. For example, the time delay canbe at least four hundred microseconds. The four hundred microseconddelay is suitable for the charge packet transfer from the photodetectorsbecause the voltage change at time T1 happens once per image. A timedelay of any length can be used in other embodiments in accordance withthe invention.

At time T2, the transfer clock signal V_(TR) is applied to gateelectrodes V1 and V7 while the accumulation clock signal V_(ACC) isapplied to gate electrodes V4 and V10. Gate electrodes V1, V4, V7, andV10 are the gate electrodes clocked by the intermediate clock signalV_(INT) at the previous time step (time T1). The charge packets in thephotodetectors associated with gate electrodes V1 and V7 transfer torespective shift register elements in the VCCD shift registers inresponse to the application of the V_(TR) clock signal. If gateelectrode V1 is associated with row 1 and gate electrode V7 with row 4,the charge packets in the photodetectors in rows 1 and 4 transfer to thevertical CCD shift registers. The voltage transitions of V_(TR) on gateelectrodes V1 and V7 are compensated fully by the voltage transitions ofV_(ACC) on gate electrodes V4 and V10.

The 0 volt voltage level shown in FIG. 10 is an intermediate clocksignal V_(INT) that is applied to four gate electrodes V1, V7, V4, andV10 at time T1. The falling edge of V_(INT) on gate electrodes V4, V10at time T2 has a voltage change of −9 volts. Thus, the −9 volt voltagechange on gate electrodes V4 and V10 fully compensated by the +9 voltvoltage change on gate electrodes V1 and V7.

At time T3, the transfer clock signal V_(TR) is applied to gateelectrodes V3 and V9 while the accumulation clock signal V_(ACC) isapplied to gate electrodes V1 and V7. Gate electrodes V1 and V7 are thegate electrodes clocked by the transfer clock signal V_(TR), at theprevious time step (time T2). The charge packets in the photodetectorsassociated with gate electrodes V3 and V9 transfer to respective shiftregister elements in the VCCD shift registers in response to theapplication of the V_(TR) clock signal. If gate electrode V3 isassociated with row 2 and gate electrode V9 with row 5, the chargepackets in the photodetectors in rows 2 and 5 transfer to the VCCD shiftregisters. The voltage transitions of V_(TR) on gate electrodes V3 andV9 are compensated fully by the voltage transitions of V_(ACC) on gateelectrodes V1 and V7.

At time T4, the transfer clock signal V_(TR) is applied to gateelectrodes V5 and V11 while the accumulation clock signal V_(ACC) isapplied to gate electrodes V3 and V9. Gate electrodes V3 and V9 are thegate electrodes clocked by V_(TR) at the previous time step (time T3).The charge packets in the photodetectors associated with gate electrodesV5 and V11 transfer to respective shift register elements the VCCD shiftregister in response to the application of the V_(TR) clock signal. Ifgate electrode V5 is associated with row 3 and gate electrode V11 withrow 6, the charge packets in the photodetectors in rows 3 and 6 transferto the VCCD shift registers. The voltage transitions of V_(TR) on gateelectrodes V5 and V11 are fully compensated by the voltage transitionsof V_(ACC) on gate electrodes V3 and V9.

At time T5, the accumulation clock signal V_(ACC) is applied to gateelectrodes V5 and V11. Gate electrodes V5 and V11 are the gateelectrodes clocked by V_(TR) at the previous time step (time T4). Thevoltage transitions on gate electrodes V5 and V11 is −18 volts. Thisvoltage transition is not compensated by any other voltage changes, soanother time delay is used in the illustrated embodiment. A time delayof at least four hundred microseconds can be used. A time delay of anylength can be used in other embodiments in accordance with theinvention.

The photodetectors are read out in three separate time steps in theembodiment shown in FIG. 10. The charge packets in a fraction of thephotodetectors transfer to respective shift register elements in theVCCD shift registers. In the illustrated embodiment, the charge packetsin one third of the photodetectors transfer to the VCCD shift registersbetween times T2 and T3. The charge packets in another one third of thephotodetectors transfer to the VCCD shift registers between times T3 andT4. And the charge packets in the remaining one third of thephotodetectors transfer to the VCCD shift registers between times T4 andT5.

Other embodiments in accordance with the invention can read out thephotodetectors using any fraction. The total number of rows read out isa multiple of the fraction that is read out. For example, in theembodiment illustrated in FIG. 7, a total of six rows of photodetectorsare read out with one third of the rows read out at one time. Three is amultiple of six (2×3). In another embodiment, one half of the six rowsof photodetectors (i.e., three rows) can be read out at one time becausetwo is a multiple of six.

Referring now to FIG. 11, there is shown a second example of a clockingdiagram for transferring charge packets from the photodetectors torespective shift register elements in the VCCD shift registers in aninterline CCD image sensor in an embodiment in accordance with theinvention. The clocking diagram is suitable for use in a CCD imagesensor having four gate electrodes (N=4) in each group of gateelectrodes. The clocking diagram is described in conjunction withtwo-phase (M=2) VCCD shift registers shown in FIG. 7.

Prior to time T1, the accumulation clock signal V_(ACC) is applied toall of the gate electrodes to place the gate electrodes in accumulationmode. To transfer charge packets from the photodetectors to the VCCDshift registers, a large voltage change must be applied to a fraction ofthe gate electrodes (e.g., half of the gate electrodes) because all ofthe gate electrodes are in accumulation mode. By way of example only,when V_(ACC) is −9 volts and a transfer clock signal V_(TR) of +9 voltsis needed to transfer charge from the photodetectors, a voltagetransition of +18 volts must be applied to half of the gate electrodesto transfer the charge from the photodetectors to respective shiftregister elements in the VCCD shift registers. The +18 volt voltagetransition can produce a large amount of undesirable well bounce. Theclocking diagram shown in FIG. 11 reduces the amount of well bounce whentransferring charge packets from the photodetectors to the VCCD shiftregisters.

At time T1, an intermediate clock signal V_(INT) is applied to gateelectrodes V1 and V3. V1 and V3 have uncompensated rising edges at timeT1 because there is no voltage change on the remaining gate electrodesV2 and V4. The voltage transition on gate electrodes V1 and V3 is +9volts (from −9 volts to 0 volts). This voltage transition is notcompensated by any other voltage changes, so a time delay is used toallow the well to settle before the next voltage change occurs at timeT2. In the illustrated embodiment, a time delay of at least one hundredmicroseconds between time T1 and time T2 allows the well to settle. Theone hundred microsecond delay is suitable for the charge transfer fromthe photodetectors because the voltage change at time T1 happens onceper image. A time delay of any length can be used in other embodimentsin accordance with the invention.

Even though the gate electrodes are not disposed over (or cover) thephotodetectors (see FIG. 6B) in an embodiment in accordance with theinvention, the gate electrodes are adjacent to the photodetectors andthe electric fields from the gate electrodes can influence the chargecapacity of the photodetectors. The voltage level of the substrate clocksignal (V_(SUB)) applied to the substrate changes by some amount at timeT1 because when the accumulation clock signal V_(ACC) is applied to allof the gate electrodes (e.g., −9 volts), the photodetectors have morecharge capacity than when half of the gate electrodes are clocked by theintermediate clock signal V_(INT) (e.g., 0 volts). In image sensorshaving a vertical overflow drain, the voltage level of the substrateclock signal V_(SUB) controls the charge capacity of the photodetectors.Increasing the substrate voltage reduces the photodetector chargecapacity while decreasing the substrate voltage increases thephotodetector charge capacity. So when V1 and V3 are clocked by theintermediate clock signal V_(INT), the voltage level applied to thesubstrate changes from V_(SUB1) to V_(SUB2) to avoid having some of thecharge in the photodetectors spill into an overflow drain. By way ofexample only, there is a two volt difference between V_(SUB1) andV_(SUB2) in an embodiment in accordance with the invention.

At time T2, the transfer clock signal V_(TR) is applied to gateelectrode V1 while the accumulation clock signal V_(ACC) is applied togate electrode V3. The voltage of the substrate clock signal V_(SUB)also transitions from V_(SUB2) to V_(SUB1). Gate electrodes V1 and V3are the gate electrodes clocked by V_(INT) at the previous time step(time T1). In the illustrated embodiment, the voltage on gate electrodeV1 transitions from 0 volts to +9 volts and the voltage on gateelectrode V3 transitions from 0 volts to −9 volts. The voltagetransition of V_(TR) (the rising edge) on gate electrode V1 iscompensated fully by the voltage transition of V_(ACC) (the fallingedge) on gate electrode V3.

Charge packets are transferred from the photodetectors associated withgate electrode V1 in response to the application of the transfer clocksignal V_(TR) (not shown). If gate electrode V1 is associated with row1, the charge packets in the photodetectors in row 1 transfer torespective shift register elements in the VCCD shift registers.

At time T3, the transfer clock signal V_(TR) is applied to gateelectrode V3 while the accumulation clock signal V_(ACC) is applied togate electrode V1. Gate electrode V1 is the gate electrode clocked byV_(TR) at the previous time step (time T2). The charge packets in thephotodetectors associated with gate electrode V3 transfer to respectiveshift register elements in the VCCD shift registers in response to theapplication of the transfer clock signal V_(TR). If gate electrode V3 isassociated with row 2, the charge packets in the photodetectors in row 2transfer to the VCCD shift registers (not shown). The voltage transitionof V_(TR) (the rising edge) on gate electrode V3 is compensated fully bythe voltage transition of V_(ACC) (the falling edge) on gate electrodeV1.

At time T4, the accumulation clock signal V_(ACC) is applied to gateelectrode V3. Gate electrode V3 is the gate electrode clocked by V_(TR)at the previous time step (time T3). The voltage on gate electrode V3transitions from +9 volts to −9 volts. This voltage change is notcompensated by any other voltage changes, so another time delay is usedto allow the well to settle before the next voltage change. A time delayof at least one hundred microseconds is used in one embodiment. A timedelay of any length can be used in other embodiments in accordance withthe invention.

There are two operating modes for a CCD image sensor in anotherembodiment in accordance with the invention. One mode is an accumulationmode where an accumulation clock signal is applied to all of the gateelectrodes. This mode is illustrated prior to time T1 and at time T5 inFIG. 10 and prior to time T1 and at time T4 in FIG. 11. Minoritycarriers (e.g., holes) accumulate at the surface of the buried channelin the VCCD shift registers during the accumulation mode.

The other mode is a charge transfer mode. The charge transfer modeincludes two phases, an initial charge transfer phase followed by afinal charge transfer phase. The initial charge transfer phase isdepicted at times T1-T2 in FIGS. 10 and 11. During the initial chargetransfer phase, at one time step an intermediate clock signal V_(INT) isapplied to a fraction of the gate electrodes in each distinct group ofgate electrodes while substantially simultaneously applying theaccumulation clock signal V_(ACC) to the remaining gate electrodes ineach distinct group of gate electrodes. At the next time step, a chargetransfer clock signal V_(TR) is applied to at least one of the gateelectrodes previously clocked by the intermediate clock signal V_(INT)while the accumulation clock signal V_(ACC) is applied to the other gateelectrode or gate electrodes previously clocked by the intermediateclock signal V_(INT). At the second time step in the initial chargetransfer phase, the voltage transition of V_(TR) (the rising edge) iscompensated fully by the voltage transition of V_(ACC) (the fallingedge). The magnitude of the voltage transition in one direction orpolarity (e.g., positive) on the at least one gate electrode iscompensated by an equal magnitude voltage transition in an oppositedirection or polarity (e.g., negative) on the other gate electrode orgate electrodes in each distinct group of gate electrodes.

The final charge transfer phase is depicted at times T3-T4 in FIG. 10and at time T3 in FIG. 11. During the final charge shifting phase, thetransfer clock signal V_(TR) is applied successively or cyclically to adifferent one gate electrode in each distinct group of gate electrodesat each time step while substantially simultaneously applying theaccumulation clock signal V_(ACC) to the gate electrode clocked by thetransfer clock signal V_(TR) at the previous time step and whilemaintaining the accumulation clock signal V_(ACC) on the remaining gateelectrodes in each distinct group of gate electrodes. During this finaltransfer phase, the voltage transition of V_(TR) (the rising edge) iscompensated fully by the voltage transition of V_(ACC) (the fallingedge). The magnitude of the voltage transition in one direction orpolarity (e.g., positive) on the one gate electrode in each distinctgroup of gate electrodes is compensated by an equal magnitude voltagetransition in an opposite direction or polarity (e.g., negative) onanother gate electrode in each distinct group of gate electrodes.

During the final charge transfer phase, the different clock signals aredetermined so that the sum of products of the capacitances and voltagechanges for at least a portion of a clocking cycle is substantially zero(ΣC_(n)ΔV_(n)≈0).

The invention has been described in detail with particular reference tocertain embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention. For example, voltage levels other than −10 volts, −9 volts, 0volts, and +9 volts can be used in other embodiments. Additionally,interline CCD image sensors can be produced with a p-type buried channeland an n-type layer. In these embodiments, the voltage levels ofV_(ACC), V_(DEP), V_(INT), V_(TR), and V_(COMP) flip such that thepositive voltages become more negative and the negative voltages becomemore positive. For example, the equation V_(COMP)<V_(ACC)<V_(DEP)becomes V_(COMP)>V_(ACC)>V_(DEP). Embodiments of the invention can beused in other types of CCD image sensors, such as, for example, fullframe CCD image sensors.

And even though specific embodiments of the invention have beendescribed herein, it should be noted that the application is not limitedto these embodiments. In particular, any features described with respectto one embodiment may also be used in other embodiments, wherecompatible. And the features of the different embodiments may beexchanged, where compatible. For example, embodiments in accordance withthe invention can use the accumulation mode, the charge shifting mode,and the charge transfer mode together, in different combinations, orindependently.

1. A charge-coupled device (CCD) image sensor includes vertical CCDshift registers and gate electrodes disposed over the vertical CCD shiftregisters, where the gate electrodes are divided into distinct groups ofgate electrodes. A method for operating the CCD image sensor includesapplying, at a first time step, an accumulation clock signal having afirst voltage level to all of the gate electrodes disposed over thevertical CCD shift registers for accumulating minority charge carriers;applying, at a second time step, a depletion clock signal having adifferent second voltage level to a respective one of the gateelectrodes in each distinct group of gate electrodes while substantiallysimultaneously applying a compensation clock signal having a differentthird voltage level to all of the remaining gate electrodes in eachdistinct group of gate electrodes, where a difference between the firstvoltage level and the second voltage level applied to the respective oneof the gate electrodes is compensated by a collective voltage differencebetween the first voltage level and the third voltage level applied tothe remaining gate electrodes in each distinct repeating group of gateelectrodes; and applying, at a third time step, the depletion clocksignal having the second voltage level to another respective one of thegate electrodes in each distinct group of gate electrodes whilesubstantially simultaneously applying the compensation clock signalhaving the third voltage level to the respective one of the gateelectrodes clocked by the depletion clock signal at the second time stepin each distinct group of gate electrodes, where a difference betweenthe third voltage level and the second voltage level applied to theanother respective one of the gate electrodes is compensated by adifference between the second voltage level and the third voltage levelapplied to the previous respective one of the gate electrodes.

2. The method in clause 1 can further include after the third time step,repeating for each remaining gate electrode in each distinct group ofgate electrodes, applying the depletion clock signal having the secondvoltage level to a different respective one of the gate electrodes ineach distinct group of gate electrodes while substantiallysimultaneously applying the compensation clock signal having the thirdvoltage level to the respective one of the gate electrodes clocked bythe depletion clock signal at the previous time step, where a differencebetween the third voltage level and the second voltage level applied tothe different respective one of the gate electrodes is compensated by adifference between the second voltage level and the third voltage levelapplied to the respective one of the gate electrodes clocked by thedepletion clock signal at the previous time step.

3. The method in clause 2 can further include after all of the gateelectrodes in each distinct group of gate electrodes is clocked by thedepletion clock signal, applying the accumulation clock signal havingthe first voltage level to all of the gate electrodes.

4. The method as in any one of the clause 1-3, where the differencebetween the first voltage level and the second voltage level applied tothe respective one of the gate electrodes is partially compensated bythe collective voltage difference between the first voltage level andthe third voltage level applied to the remaining gate electrodes in eachdistinct repeating group of gate electrodes.

5. The method as in any one of the clauses 1-3, wherein the differencebetween the first voltage level and the second voltage level applied tothe respective one of the gate electrodes is fully compensated by thecollective voltage difference between the first voltage level and thethird voltage level applied to the remaining gate electrodes in eachdistinct repeating group of gate electrodes.

6. A charge-coupled device (CCD) image sensor includes vertical CCDshift registers and gate electrodes disposed over the vertical CCD shiftregisters and the gate electrodes are divided into distinct repeatinggroups of gate electrodes. A method for operating the CCD image sensorincludes applying, at a first time step, an accumulation clock signalhaving a first voltage level to all of the gate electrodes; applying, ata second time step, a depletion clock signal having a different secondvoltage level to a respective one of the gate electrodes in eachdistinct repeating group of gate electrodes while substantiallysimultaneously applying a compensation clock signal having a differentthird voltage level to the remaining gate electrodes in each distinctrepeating group of gate electrodes, where the first voltage level of theaccumulation clock signal is between the third voltage level of thecompensation clock signal and the second voltage level of the depletionclock signal.

7. The method in clause 6 can further include after the third time step,repeating for each remaining gate electrode in each distinct group ofgate electrodes, applying the depletion clock signal having the secondvoltage level to a different respective one of the gate electrodes ineach distinct group of gate electrodes while substantiallysimultaneously applying the compensation clock signal having the thirdvoltage level to the respective one of the gate electrodes clocked bythe depletion clock signal at the previous time step.

8. A charge-coupled device (CCD) image sensor is adapted to operate in acharge shifting mode and in an accumulation mode. The CCD image sensorincludes vertical CCD shift registers and gate electrodes disposed overthe vertical CCD shift registers and the gate electrodes are dividedinto distinct groups of gate electrodes. A method for operating the CCDimage sensor includes in an initial charge shifting phase of the chargeshifting mode, applying a depletion clock signal to one gate electrodein each distinct group of gate electrodes while substantiallysimultaneously applying a compensation clock signal to all of theremaining gate electrodes in each distinct group of gate electrodes,where a collective voltage transition of the compensation clock signalon the remaining gate electrodes in each distinct group of gateelectrodes compensates for a voltage transition of the depletion clocksignal on the one gate electrode in each distinct group of gateelectrodes; and in a final charge shifting phase of the charge shiftingmode, applying the depletion clock signal successively to a differentone gate electrode in each distinct group of gate electrodes whilesubstantially simultaneously applying the compensation clock signal tothe gate electrode clocked by the depletion clock signal at the previoustime step and maintaining the compensation clock signal on the remaininggate electrodes in each distinct group of gate electrodes, where avoltage transition of the compensation clock signal on the gateelectrode previously clocked by the depletion clock signal substantiallycompensates for a voltage transition of the depletion clock signal oneach different one gate electrode in each distinct group of gateelectrodes.

9. The method in clause 8 can further include in the accumulation mode,applying an accumulation clock signal to all of the gate electrodes.

10. The method as in clause 8 or clause 9, where the collective voltagetransition of the compensation clock signal on the remaining gateelectrodes in each distinct group of gate electrodes partiallycompensates for a voltage transition of the depletion clock signal onthe one gate electrode in each distinct group of gate electrodes.

11. The method as in clause 8 or clause 9, where the collective voltagetransition of the compensation clock signal on the remaining gateelectrodes in each distinct group of gate electrodes fully compensatesfor a voltage transition of the depletion clock signal on the one gateelectrode in each distinct group of gate electrodes.

12. A CCD image sensor includes photodetectors, vertical CCD shiftregisters, and gate electrodes disposed over the vertical CCD shiftregisters. The gate electrodes are divided into distinct repeatinggroups of gate electrodes. A method for operating the CCD image sensorincludes applying at a first time step an intermediate clock signalhaving a first voltage level to a fraction of the gate electrodes ineach distinct repeating group of gate electrodes; and transferringcharge packets from a fraction of the photodetectors to respectivevertical CCD shift registers by applying at a second time step atransfer clock signal having a different second voltage level to afraction of the gate electrodes clocked by the intermediate clock signalat the first time step and applying an accumulation clock signal havinga different third voltage level to the remaining portion of the gateelectrodes clocked by the intermediate clock signal at the first timestep such that a voltage transition on the gate electrodes clocked bythe accumulation clock signal substantially compensates a voltagetransition on the gate electrodes clocked by the transfer clock signal.

13. The method in clause 12 can further include transferring chargepackets from another fraction of the photodetectors to respectivevertical CCD shift registers by applying at a third time step a transferclock signal to a fraction of the gate electrodes clocked by theaccumulation clock signal and applying the accumulation clock signal tothe fraction of the gate electrodes clocked by the transfer clock signalat the second time step such that a voltage transition on the portion ofthe gate electrodes clocked by the accumulation clock signalsubstantially compensates a voltage transition on the portion of thegate electrodes clocked by the transfer clock signal.

14. The method in clause 12 or in clause 13 can further includetransitioning a voltage level applied to a substrate from a firstvoltage level to a second voltage level substantially simultaneouslywith the application of the intermediate clock signal at the first timestep.

15. The method in clause 14 can further include transitioning thevoltage level applied to a substrate from the second voltage level tothe first voltage level substantially simultaneously with theapplication of the transfer clock signal at the second time step.

16. A charge-coupled device (CCD) image sensor is adapted to operate ina charge transfer mode and in an accumulation mode. The CCD image sensorincludes vertical CCD shift registers and gate electrodes disposed overthe vertical CCD shift registers. The gate electrodes are divided intodistinct groups of gate electrodes. A method for operating the CCD imagesensor includes in an initial charge transfer phase of the chargetransfer mode, applying at a first time step an intermediate clocksignal to a fraction of the gate electrodes in each distinct group ofgate electrodes while substantially simultaneously applying anaccumulation clock signal to the remaining gate electrodes in eachdistinct group of gate electrodes, and applying at a second time step atransfer clock signal to at least one of the gate electrodes in eachdistinct group of gate electrodes clocked by the intermediate clocksignal at the first time step while substantially simultaneouslyapplying the accumulation clock signal to the remaining gate electrodesin each distinct group of gate electrodes clocked by the intermediateclock signal at the first time step, where a voltage transition of theaccumulation clock signal applied to the remaining gate electrodes ineach distinct group of gate electrodes compensates for a voltagetransition of the transfer clock signal applied to at least one of thegate electrodes in each distinct group of gate electrodes; and in afinal charge transfer phase of the charge transfer mode, at eachsubsequent time step applying the transfer clock signal successively toa different fraction of the gate electrodes in each distinct group ofgate electrodes while substantially simultaneously applying theaccumulation clock signal to each gate electrode clocked by the transferclock signal at the previous time step and maintaining the accumulationclock signal on the remaining gate electrodes in each distinct group ofgate electrodes, where a voltage transition of the accumulation clocksignal applied to each gate electrode clocked by the transfer clocksignal at the previous time step compensates a voltage transition of thetransfer clock signal.

17. The method in clause 16 can further include in the accumulationmode, applying an accumulation clock signal to all of the gateelectrodes.

18. The method in clause 16 or in clause 17 can further includetransitioning a voltage level applied to a substrate from a firstvoltage level to a second voltage level substantially simultaneouslywith the application of the intermediate clock signal at the first timestep.

19. The method in clause 18 can further include transitioning thevoltage level applied to a substrate from the second voltage level tothe first voltage level substantially simultaneously with theapplication of the transfer clock signal at the second time step.

20. The method in clause 19 can further include in the accumulationmode, applying an accumulation clock signal to all of the gateelectrodes.

21. The method as in any one of the clauses 16-20, where the CCD imagesensor is further adapted to operate in a charge shifting mode.

22. The method as in clause 21 can further include in an initial chargeshifting phase of the charge shifting mode, applying a depletion clocksignal to one gate electrode in each distinct group of gate electrodeswhile substantially simultaneously applying a compensation clock signalto the remaining gate electrodes in each distinct group of gateelectrodes, where a collective voltage transition of the compensationclock signal on the remaining gate electrodes in each distinct group ofgate electrodes compensates for a voltage transition of the depletionclock signal on the one gate electrode in each distinct group of gateelectrodes; and in a final charge shifting phase of the charge shiftingmode, at each subsequent time step applying the depletion clock signalsuccessively to a different one gate electrode in each distinct group ofgate electrodes while substantially simultaneously applying thecompensation clock signal to the gate electrode clocked by the depletionclock signal at the previous clock signal and maintaining thecompensation clock signal on the remaining gate electrodes in eachdistinct group of gate electrodes, where a voltage transition of thecompensation clock signal on the gate electrode previously clocked bythe depletion clock signal substantially compensates for a voltagetransition of the depletion clock signal on each different one gateelectrode in each distinct group of gate electrodes.

23. The method in clause 22 can further include in the accumulationmode, applying an accumulation clock signal to all of the gateelectrodes.

24. A charge-coupled device (CCD) image sensor includes vertical CCDshift registers and gate electrodes disposed over the vertical CCD shiftregisters. The gate electrodes are divided into distinct groups of gateelectrodes. The CCD image sensor includes means for applying, at a firsttime step, an accumulation clock signal having a first voltage level toall of the gate electrodes disposed over the vertical CCD shiftregisters for accumulating minority charge carriers; means for applying,at a second time step, a depletion clock signal having a differentsecond voltage level to a respective one of the gate electrodes in eachdistinct group of gate electrodes while substantially simultaneouslyapplying a compensation clock signal having a different third voltagelevel to all of the remaining gate electrodes in each distinct group ofgate electrodes, where a difference between the first voltage level andthe second voltage level applied to the respective one of the gateelectrodes is compensated by a collective voltage difference between thefirst voltage level and the third voltage level applied to the remaininggate electrodes in each distinct repeating group of gate electrodes; andmeans for applying, at a third time step, the depletion clock signalhaving the second voltage level to another respective one of the gateelectrodes in each distinct group of gate electrodes while substantiallysimultaneously applying the compensation clock signal having the thirdvoltage level to the respective one of the gate electrodes clocked bythe depletion clock signal at the second time step in each distinctgroup of gate electrodes, where a difference between the third voltagelevel and the second voltage level applied to the another respective oneof the gate electrodes is compensated by a difference between the secondvoltage level and the third voltage level applied to the previousrespective one of the gate electrodes.

25. The CCD image sensor in clause 24 can further include after thethird time step, means for applying to each remaining gate electrode ineach distinct group of gate electrodes the depletion clock signal havingthe second voltage level to a different respective one of the gateelectrodes in each distinct group of gate electrodes while substantiallysimultaneously applying the compensation clock signal having the thirdvoltage level to the respective one of the gate electrodes clocked bythe depletion clock signal at the previous time step, where a differencebetween the third voltage level and the second voltage level applied tothe different respective one of the gate electrodes is compensated by adifference between the second voltage level and the third voltage levelapplied to the respective one of the gate electrodes clocked by thedepletion clock signal at the previous time step.

26. The CCD image sensor in clause 25 can further include after all ofthe gate electrodes in each distinct group of gate electrodes is clockedby the depletion clock signal, means for applying the accumulation clocksignal having the first voltage level to all of the gate electrodes.

27. The CCD image sensor as in any one of clauses 24-26, where thedifference between the first voltage level and the second voltage levelapplied to the respective one of the gate electrodes is partiallycompensated by the collective voltage difference between the firstvoltage level and the third voltage level applied to the remaining gateelectrodes in each distinct repeating group of gate electrodes.

28. The CCD image sensor as in any one of clauses 24-26, where thedifference between the first voltage level and the second voltage levelapplied to the respective one of the gate electrodes is fullycompensated by the collective voltage difference between the firstvoltage level and the third voltage level applied to the remaining gateelectrodes in each distinct repeating group of gate electrodes.

29. A charge-coupled device (CCD) image sensor is adapted to operate ina charge shifting mode and in an accumulation mode. The CCD image sensorincludes vertical CCD shift registers and gate electrodes disposed overthe vertical CCD shift registers. The gate electrodes are divided intodistinct groups of gate electrodes. The CCD image sensor includes in aninitial charge shifting phase of the charge shifting mode, means forapplying a depletion clock signal to one gate electrode in each distinctgroup of gate electrodes while substantially simultaneously applying acompensation clock signal to all of the remaining gate electrodes ineach distinct group of gate electrodes, where a collective voltagetransition of the compensation clock signal on the remaining gateelectrodes in each distinct group of gate electrodes compensates for avoltage transition of the depletion clock signal on the one gateelectrode in each distinct group of gate electrodes; and in a finalcharge shifting phase of the charge shifting mode, means for applyingthe depletion clock signal successively to a different one gateelectrode in each distinct group of gate electrodes while substantiallysimultaneously applying the compensation clock signal to the gateelectrode clocked by the depletion clock signal at the previous timestep and maintaining the compensation clock signal on the remaining gateelectrodes in each distinct group of gate electrodes, where a voltagetransition of the compensation clock signal on the gate electrodepreviously clocked by the depletion clock signal substantiallycompensates for a voltage transition of the depletion clock signal oneach different one gate electrode in each distinct group of gateelectrodes.

30. The CCD image sensor in clause 29 can further include in theaccumulation mode, means for applying an accumulation clock signal toall of the gate electrodes.

31. The CCD image sensor as in clause 29 or clause 30, where thecollective voltage transition of the compensation clock signal on theremaining gate electrodes in each distinct group of gate electrodespartially compensates for a voltage transition of the depletion clocksignal on the one gate electrode in each distinct group of gateelectrodes.

32. The CCD image sensor as in clause 29 or clause 30, where thecollective voltage transition of the compensation clock signal on theremaining gate electrodes in each distinct group of gate electrodesfully compensates for a voltage transition of the depletion clock signalon the one gate electrode in each distinct group of gate electrodes.

33. A charge-coupled device (CCD) image sensor includes photodetectorsand vertical CCD shift registers with gate electrodes disposed over thevertical CCD shift registers. The gate electrodes are divided intodistinct groups of gate electrodes. The CCD image sensor includes: meansfor applying at a first time step an intermediate clock signal having afirst voltage level to a fraction of the gate electrodes in eachdistinct group of gate electrodes; and means for applying at a secondtime step a transfer clock signal having a different second voltagelevel to a fraction of the gate electrodes clocked by the intermediateclock signal at the first time step and applying an accumulation clocksignal having a different third voltage level to the remaining portionof the gate electrodes clocked by the intermediate clock signal at thefirst time step such that a voltage transition on the gate electrodesclocked by the accumulation clock signal substantially compensates avoltage transition on the gate electrodes clocked by the transfer clocksignal.

34. The CCD image sensor in clause 33 can further include means forapplying at a third time step a transfer clock signal to a fraction ofthe gate electrodes clocked by the accumulation clock signal andapplying the accumulation clock signal to the fraction of the gateelectrodes clocked by the transfer clock signal at the second time stepsuch that a voltage transition on the portion of the gate electrodesclocked by the accumulation clock signal substantially compensates avoltage transition on the portion of the gate electrodes clocked by thetransfer clock signal.

35. The CCD image sensor in clause 33 or in clause 34 can furtherinclude means for transitioning a voltage level applied to a substratefrom a first voltage level to a second voltage level substantiallysimultaneously with the application of the intermediate clock signal atthe first time step.

36. The CCD image sensor in clause 35 can further include means fortransitioning the voltage level applied to a substrate from the secondvoltage level to the first voltage level substantially simultaneouslywith the application of the transfer clock signal at the second timestep.

37. A charge-coupled device (CCD) image sensor is adapted to operate ina charge transfer mode and in an accumulation mode. The CCD image sensorincludes vertical CCD shift registers and gate electrodes disposed overthe vertical CCD shift registers. The gate electrodes are divided intodistinct groups of gate electrodes, The CCD image sensor includes in aninitial charge transfer phase of the charge transfer mode, means forapplying at a first time step an intermediate clock signal to a fractionof the gate electrodes in each distinct group of gate electrodes whilesubstantially simultaneously applying an accumulation clock signal tothe remaining gate electrodes in each distinct group of gate electrodes,and means for applying at a second time step a transfer clock signal toat least one of the gate electrodes in each distinct group of gateelectrodes clocked by the intermediate clock signal at the first timestep while substantially simultaneously applying the accumulation clocksignal to the remaining gate electrodes in each distinct group of gateelectrodes clocked by the intermediate clock signal at the first timestep, where a voltage transition of the accumulation clock signalapplied to the remaining gate electrodes in each distinct group of gateelectrodes compensates for a voltage transition of the transfer clocksignal applied to at least one of the gate electrodes in each distinctgroup of gate electrodes; and in a final charge transfer phase of thecharge transfer mode, means for applying at each subsequent time stepthe transfer clock signal successively to a different fraction of thegate electrodes in each distinct group of gate electrodes whilesubstantially simultaneously applying the accumulation clock signal toeach gate electrode clocked by the transfer clock signal at the previoustime step and maintaining the accumulation clock signal on the remaininggate electrodes in each distinct group of gate electrodes, where avoltage transition of the accumulation clock signal applied to each gateelectrode clocked by the transfer clock signal at the previous time stepcompensates a voltage transition of the transfer clock signal.

38. The CCD image sensor in clause 37 can further include in theaccumulation mode, means for applying an accumulation clock signal toall of the gate electrodes.

39. The CCD image sensor in clause 37 or in clause 38 can furtherinclude means for transitioning a voltage level applied to a substratefrom a first voltage level to a second voltage level substantiallysimultaneously with the application of the intermediate clock signal atthe first time step.

40. The CCD image sensor in clause 39 can further include means fortransitioning the voltage level applied to a substrate from the secondvoltage level to the first voltage level substantially simultaneouslywith the application of the transfer clock signal at the second timestep.

41. The CCD image sensor in clause 40 can further include in theaccumulation mode, means for applying an accumulation clock signal toall of the gate electrodes.

42. The CCD image sensor as in any one of clauses 37-41, where the CCDimage sensor is further adapted to operate in a charge shifting mode.

43. The CCD image sensor in clause 42 can further include in an initialcharge shifting phase of the charge shifting mode, means for applying adepletion clock signal to one gate electrode in each distinct group ofgate electrodes while substantially simultaneously applying acompensation clock signal to the remaining gate electrodes in eachdistinct group of gate electrodes, where a collective voltage transitionof the compensation clock signal on the remaining gate electrodes ineach distinct group of gate electrodes compensates for a voltagetransition of the depletion clock signal on the one gate electrode ineach distinct group of gate electrodes; and in a final charge shiftingphase of the charge shifting mode, means for applying at each subsequenttime step the depletion clock signal successively to a different onegate electrode in each distinct group of gate electrodes whilesubstantially simultaneously applying the compensation clock signal tothe gate electrode clocked by the depletion clock signal at the previousclock signal and maintaining the compensation clock signal on theremaining gate electrodes in each distinct group of gate electrodes,where a voltage transition of the compensation clock signal on the gateelectrode previously clocked by the depletion clock signal substantiallycompensates for a voltage transition of the depletion clock signal oneach different one gate electrode in each distinct group of gateelectrodes.

44. The CCD image sensor in clause 43 can further include in theaccumulation mode, means for applying an accumulation clock signal toall of the gate electrodes.

45. A charge-coupled device (CCD) image sensor is adapted to operate ina charge transfer mode and in an accumulation mode. The CCD image sensorincludes vertical CCD shift registers and gate electrodes disposed overthe vertical CCD shift registers. The gate electrodes are divided intodistinct groups of gate electrodes, The CCD image sensor includes in aninitial charge transfer phase of the charge transfer mode, means forapplying at a first time step an intermediate clock signal to a fractionof the gate electrodes in each distinct group of gate electrodes whilesubstantially simultaneously applying an accumulation clock signal tothe remaining gate electrodes in each distinct group of gate electrodes,and means for applying at a second time step a transfer clock signal toat least one of the gate electrodes in each distinct group of gateelectrodes clocked by the intermediate clock signal at the first timestep while substantially simultaneously applying the accumulation clocksignal to the remaining gate electrodes in each distinct group of gateelectrodes clocked by the intermediate clock signal at the first timestep, where the transfer and accumulation clock signals applied to thegate electrodes at the second time step are determined so that a sum ofproducts of capacitances and voltage changes is substantially zero; andin a final charge transfer phase of the charge transfer mode, means forapplying at each subsequent time step the transfer clock signalsuccessively to a different fraction of the gate electrodes in eachdistinct group of gate electrodes while substantially simultaneouslyapplying the accumulation clock signal to each gate electrode clocked bythe transfer clock signal at the previous time step and maintaining theaccumulation clock signal on the remaining gate electrodes in eachdistinct group of gate electrodes, where the transfer and accumulationclock signals applied to the gate electrodes in each distinct group ofgate electrodes are determined so that a sum of products of capacitancesand voltage changes is substantially zero.

46. The CCD image sensor in clause 45 can further include in theaccumulation mode, means for applying an accumulation clock signal toall of the gate electrodes.

47. The CCD image sensor in clause 45 or in clause 46 can furtherinclude means for transitioning a voltage level applied to a substratefrom a first voltage level to a second voltage level substantiallysimultaneously with the application of the intermediate clock signal atthe first time step.

48. The CCD image sensor in clause 47 can further include means fortransitioning the voltage level applied to a substrate from the secondvoltage level to the first voltage level substantially simultaneouslywith the application of the transfer clock signal at the second timestep.

49. The CCD image sensor in clause 48 can further include in theaccumulation mode, means for applying an accumulation clock signal toall of the gate electrodes.

50. The CCD image sensor as in any one of clauses 45-49, where the CCDimage sensor is further adapted to operate in a charge shifting mode.

51. The CCD image sensor in clause 50 can further include in an initialcharge shifting phase of the charge shifting mode, means for applying adepletion clock signal to one gate electrode in each distinct group ofgate electrodes while substantially simultaneously applying acompensation clock signal to the remaining gate electrodes in eachdistinct group of gate electrodes, where the depletion and compensationclock signals applied to the gate electrodes are determined so that asum of products of capacitances and voltage changes is substantiallyzero; and in a final charge shifting phase of the charge shifting mode,means for applying at each subsequent time step the depletion clocksignal successively to a different one gate electrode in each distinctgroup of gate electrodes while substantially simultaneously applying thecompensation clock signal to the gate electrode clocked by the depletionclock signal at the previous clock signal and maintaining thecompensation clock signal on the remaining gate electrodes in eachdistinct group of gate electrodes, where the depletion and compensationclock signals applied to the gate electrodes are determined so that asum of products of capacitances and voltage changes is substantiallyzero.

52. The CCD image sensor in clause 51 can further include in theaccumulation mode, means for applying an accumulation clock signal toall of the gate electrodes.

53. A charge-coupled device (CCD) image sensor is adapted to operate ina charge shifting mode and in an accumulation mode. The CCD image sensorincludes vertical CCD shift registers and gate electrodes disposed overthe vertical CCD shift registers and the gate electrodes are dividedinto distinct groups of gate electrodes. A method for operating the CCDimage sensor includes in an initial charge shifting phase of the chargeshifting mode, applying a depletion clock signal to one gate electrodein each distinct group of gate electrodes while substantiallysimultaneously applying a compensation clock signal to all of theremaining gate electrodes in each distinct group of gate electrodes,where the depletion and compensation clock signals applied to the gateelectrodes are determined so that a sum of products of capacitances andvoltage changes is substantially zero; and in a final charge shiftingphase of the charge shifting mode, applying the depletion clock signalsuccessively to a different one gate electrode in each distinct group ofgate electrodes while substantially simultaneously applying thecompensation clock signal to the gate electrode clocked by the depletionclock signal at the previous time step and maintaining the compensationclock signal on the remaining gate electrodes in each distinct group ofgate electrodes, where the depletion and compensation clock signalsapplied to the gate electrodes are determined so that a sum of productsof capacitances and voltage changes is substantially zero.

54. The method in clause 53 can further include in the accumulationmode, applying an accumulation clock signal to all of the gateelectrodes.

PARTS LIST

-   100 image sensor-   102 photodetector-   104 imaging area-   106 vertical charge-coupled device (VCCD) shift register-   108 charge packet-   110 shift register element-   112 horizontal charge-coupled device (HCCD) shift register-   114 output circuit-   200 gate electrode-   202 gate electrode-   204 substrate layer-   206 layer-   208 buried channel-   210 well contact-   400 voltage transition-   402 voltage transition-   500 image capture device-   502 light-   504 imaging stage-   506 image sensor-   508 clock driver-   510 processor-   512 memory-   514 display-   516 one or more additional input/output elements-   600 imaging area-   602 VCCD shift register-   604 photodetector-   606 gate electrode-   608 gate electrode-   610 signal lines-   612 two rows of imaging area-   700 group of gate electrodes-   702 charge packet-   704 charge packet-   706 charge packet-   708 charge packet-   710 charge packet-   712 charge packet

What is claimed is:
 1. A charge-coupled device (CCD) image sensorincluding a plurality of photodetectors and a plurality of vertical CCDshift registers, wherein gate electrodes are disposed over the verticalCCD shift registers and the gate electrodes are divided into distinctgroups of gate electrodes, the CCD image sensor comprising: means forapplying at a first time step an intermediate clock signal having afirst voltage level to a fraction of the gate electrodes in eachdistinct group of gate electrodes; and means for applying at a secondtime step a transfer clock signal having a different second voltagelevel to a fraction of the gate electrodes clocked by the intermediateclock signal at the first time step and applying an accumulation clocksignal having a different third voltage level to the remaining portionof the gate electrodes clocked by the intermediate clock signal at thefirst time step such that a voltage transition on the gate electrodesclocked by the accumulation clock signal substantially compensates avoltage transition on the gate electrodes clocked by the transfer clocksignal.
 2. The CCD image sensor as in claim 1, further comprising meansfor applying at a third time step a transfer clock signal to a fractionof the gate electrodes clocked by the accumulation clock signal andapplying the accumulation clock signal to the fraction of the gateelectrodes clocked by the transfer clock signal at the second time stepsuch that a voltage transition on the portion of the gate electrodesclocked by the accumulation clock signal substantially compensates avoltage transition on the portion of the gate electrodes clocked by thetransfer clock signal.
 3. The CCD image sensor as in claim 1, furthercomprising means for transitioning a voltage level applied to asubstrate from a first voltage level to a second voltage levelsubstantially simultaneously with the application of the intermediateclock signal at the first time step.
 4. The CCD image sensor as in claim3, further comprising means for transitioning the voltage level appliedto a substrate from the second voltage level to the first voltage levelsubstantially simultaneously with the application of the transfer clocksignal at the second time step.
 5. A charge-coupled device (CCD) imagesensor adapted to operate in a charge transfer mode and in anaccumulation mode, wherein the CCD image sensor includes a plurality ofvertical CCD shift registers and a plurality of gate electrodes disposedover the vertical CCD shift registers and the plurality of gateelectrodes are divided into distinct groups of gate electrodes, the CCDimage sensor comprising: in an initial charge transfer phase of thecharge transfer mode, means for applying at a first time step anintermediate clock signal to a fraction of the gate electrodes in eachdistinct group of gate electrodes while substantially simultaneouslyapplying an accumulation clock signal to the remaining gate electrodesin each distinct group of gate electrodes, and means for applying at asecond time step a transfer clock signal to at least one of the gateelectrodes in each distinct group of gate electrodes clocked by theintermediate clock signal at the first time step while substantiallysimultaneously applying the accumulation clock signal to the remaininggate electrodes in each distinct group of gate electrodes clocked by theintermediate clock signal at the first time step, wherein a voltagetransition of the accumulation clock signal applied to the remaininggate electrodes in each distinct group of gate electrodes compensatesfor a voltage transition of the transfer clock signal applied to atleast one of the gate electrodes in each distinct group of gateelectrodes; and in a final charge transfer phase of the charge transfermode, means for applying at each subsequent time step the transfer clocksignal successively to a different fraction of the gate electrodes ineach distinct group of gate electrodes while substantiallysimultaneously applying the accumulation clock signal to each gateelectrode clocked by the transfer clock signal at the previous time stepand maintaining the accumulation clock signal on the remaining gateelectrodes in each distinct group of gate electrodes, wherein a voltagetransition of the accumulation clock signal applied to each gateelectrode clocked by the transfer clock signal at the previous time stepcompensates a voltage transition of the transfer clock signal.
 6. TheCCD image sensor as in claim 5, further comprising in the accumulationmode, means for applying an accumulation clock signal to all of the gateelectrodes.
 7. The CCD image sensor as in claim 5, further comprisingmeans for transitioning a voltage level applied to a substrate from afirst voltage level to a second voltage level substantiallysimultaneously with the application of the intermediate clock signal atthe first time step.
 8. The CCD image sensor as in claim 7, furthercomprising means for transitioning the voltage level applied to asubstrate from the second voltage level to the first voltage levelsubstantially simultaneously with the application of the transfer clocksignal at the second time step.
 9. The CCD image sensor as in claim 8,further comprising in the accumulation mode, means for applying anaccumulation clock signal to all of the gate electrodes.
 10. The CCDimage sensor as in claim 5, wherein the CCD image sensor is furtheradapted to operate in a charge shifting mode.
 11. The CCD image sensoras in claim 10, further comprising: in an initial charge shifting phaseof the charge shifting mode, means for applying a depletion clock signalto one gate electrode in each distinct group of gate electrodes whilesubstantially simultaneously applying a compensation clock signal to theremaining gate electrodes in each distinct group of gate electrodes,wherein a collective voltage transition of the compensation clock signalon the remaining gate electrodes in each distinct group of gateelectrodes compensates for a voltage transition of the depletion clocksignal on the one gate electrode in each distinct group of gateelectrodes; and in a final charge shifting phase of the charge shiftingmode, means for applying at each subsequent time step the depletionclock signal successively to a different one gate electrode in eachdistinct group of gate electrodes while substantially simultaneouslyapplying the compensation clock signal to the gate electrode clocked bythe depletion clock signal at the previous clock signal and maintainingthe compensation clock signal on the remaining gate electrodes in eachdistinct group of gate electrodes, wherein a voltage transition of thecompensation clock signal on the gate electrode previously clocked bythe depletion clock signal substantially compensates for a voltagetransition of the depletion clock signal on each different one gateelectrode in each distinct group of gate electrodes.
 12. The CCD imagesensor as in claim 11, further comprising in the accumulation mode,means for applying an accumulation clock signal to all of the gateelectrodes.